Increasingly, matrix/fiber composite materials are being employed in applications requiring both high performance characteristics, and low weight per strength yield profiles. The increasing demand for improved composite materials, exhibiting good toughness at high temperatures is no where more keenly felt than in the military and commercial aerospace industries. As new applications are identified, new requirements are established which these composite systems must meet.
Composite systems will vary greatly with regard to the matrix resin employed, and the success or failure of this system depends, to a great extent, on the nature of the matrix resin. Both processability and chemical makeup, and the characteristics achieved thereby, are of value. Thus, a low cure time and temperature with relatively simplified processing requirements which shows a good (high) Tg are more desirable than conventional autoclave systems that cure at temperatures of 350.degree. F. and above.
Perhaps the most dominant matrix system currently available is an epoxy/amine type system. These matrix resins are combined with oriented fiber reinforcing means to form a prepreg or other tape form subsequently built up into a fabric. Alternatively, the resin is applied to a previously prepared fabric form. The epoxy/amine systems are generally desirable because of high compressive strength, high modulus and high Tg characteristics. However, these properties are lost, or substantially reduced, when the system is exposed to either moisture or excessive heat. Further, many applications call for a toughened system. To "toughen" the epoxy/amine systems available, a loss in the Tg, or solvent resistance, or some combination, is frequently encountered. Other problems plaguing the industry include the lack of consistency in the production of most systems, and the lack of a single system providing a good balance of necessary properties including relatively high compressive strength, toughness and modulus characteristics, with a good Tg, characteristics which are not extensively reduced when exposed to moisture and/or excessive heat.
Accordingly, it remains a pressing need in the industry to provide a matrix resin system, combinable with oriented reinforcing fibers of high modulus, to give composite materials of exceedingly high strength/weight characteristics, and with a balance of desirable properties.